Melissa McCarthy may now be one of the biggest female comedy stars of the moment in terms of box office but she’s in serious danger of becoming typecast. Tammy, her latest, repeats the same formula for ‘success’ that has served her ever since breaking through in Bridesmaids and which has been re-employed to hit-and-miss effect in Identity Thief and The Heat – that is to say, playing a foul-mouthed, bad attitude kind of character whose brash exterior belies a fragile soul.

Co-written by McCarthy with real-life husband Ben Falcone (who also directs and features briefly in the film as her boss), the set-up here follows the misfortunes of Tammy as she gets fired from her job, discovers her husband is having an affair and sets out on a road trip with her promiscuous, alcoholic grandmother (played by Susan Sarandon). But while allegedly a comedy, most of what subsequently occurs strikes a duff note that often feels desperate in its search for laughs.

For starters, Tammy is just not that likeable a character and her path towards redemption feels contrived and unlikely. But then everything about the film feels false, whether it’s the unconvincing central relationship between McCarthy and Sarandon – which is volatile one minute, mawkish the next – or the tepid romance that occurs between Tammy and the son of one of her grandmother’s flings (played by Mark Duplass).

The most surprising thing about the film is just what a big ensemble cast it has managed to attract – and which further extends to Toni Collette, Kathy Bates, Allison Janney and Dan Aykroyd – because no one is well served in terms of character development or script. Perhaps the biggest problem with Tammy, though, is the sense that it doesn’t really know what it wants to be: big, bawdy studio comedy or something more subtle and indie spirited, as evidenced in its final third. The result is an ill-conceived mess.

General release from Fri 4 Jul.

Tammy - Official Trailer 2 [HD]